The present invention relates to an improved process for the production of polyamine mixtures of the polyamino-polyaryl-polymethylene series, as well as to the use thereof in the production of white polyurethane foam materials.
The production of diaminoarylmethane and polyamino-polyaryl-polymethylene mixtures by the acid condensation of aromatic amine and formaldehyde is known (U.S. Pat. No. 2,683,730). The diaminoarylmethane and the polyamine mixtures are valuable as intermediate products in the production of the corresponding isocyanates. Polyurethane foams produced from such isocyanates show a yellow-brown coloration. The coloration of the foam has come to serve as a quality characteristic of the isocyanate used: the darker the coloration, the poorer the isocyanate used.
German Auslegeschrift 3,225,135 describes a process for the production of polyamino polyaryl polymethylenes in which the components are preferably mixed at temperatures of up to 50.degree. C., and in which the reaction mixture is reacted in a tube reactor at a continuously increasing temperature from 50.degree.C. until reaching from 90.degree. C. to 100.degree. C. The polyurethane foam materials produced from the corresponding isocyanates are darkly discolored.
U.S. Pat. No. 4,259,526 describes a special process for the production of polyamino polyaryl polymethylenes, in which the amine is reacted with formaldehyde in the presence of an acid catalyst at 10.degree. C. to 100.degree. C. at a protonation degree of from 0.1 to 25%. Additional acid is added subsequently, and the temperature is adjusted 75.degree. C. to 150.degree. C. The polyamine is then separated. The disadvantage of this process is the expensive separation of the acid catalyst. In addition, the polyurethane foam obtained from the corresponding isocyanate is not light in color.
The object of the present invention was therefore to discover a process which permits production of a high grade isocyanate that results in a light polyurethane foam material.